The present invention generally relates to inkjet and other types of printers and, more particularly, to the printhead portion of an inkjet printer.
Inkjet printers have gained wide acceptance. These printers are described by W. J. Lloyd and H. T. Taub in xe2x80x9cInk Jet Devices,xe2x80x9d Chapter 13 of Output Hardcopy Devices (Ed. R. C. Durbeck and S. Sherr, San Diego: Academic Press, 1988) and U.S. Pat. Nos. 4,490,728 and 4,313,684. Inkjet printers produce high quality print, are compact and portable, and print quickly and quietly because only ink strikes the paper.
An inkjet printer forms a printed image by printing a pattern of individual dots at particular locations of an array defined for the printing medium. The locations are conveniently visualized as being small dots in a rectilinear array. The locations are sometimes xe2x80x9cdot locationsxe2x80x9d, xe2x80x9cdot positionsxe2x80x9d, or pixelsxe2x80x9d. Thus, the printing operation can be viewed as the filling of a pattern of dot locations with dots of ink.
inkjet printers print dots by ejecting very small drops of ink onto the print medium and typically include a movable carriage that supports one or more printheads each having ink ejecting nozzles. The carriage traverses over the surface of the print medium, and the nozzles are controlled to eject drops of ink at appropriate times pursuant to command of a microcomputer or other controller, wherein the timing of the application of the ink drops is intended to correspond to the pattern of pixels of the image being printed.
The typical inkjet printhead (i.e., the silicon substrate, structures built on the substrate, and connections to the substrate) uses liquid ink (i.e., dissolved colorants or pigments dispersed in a solvent). It has an array of precisely formed nozzles attached to a printhead substrate that incorporates an array of firing chambers which receive liquid ink from the ink reservoir. Each chamber has a thin-film resistor, known as a inkjet firing chamber resistor, located opposite the nozzle so ink can collect between it and the nozzle. The firing of ink droplets is typically under the control of a microprocessor, the signals of which are conveyed by electrical traces to the resistor elements. When electric printing pulses heat the inkjet firing chamber resistor, a small portion of the ink next to it vaporizes and ejects a drop of ink from the printhead. Properly arranged nozzles form a dot matrix pattern. Properly sequencing the operation of each nozzle causes characters or images to be printed upon the paper as the printhead moves past the paper.
The ink cartridge containing the nozzles is moved repeatedly across the width of the medium to be printed upon. At each of a designated number of increments of this movement across the medium, each of the nozzles is caused either to eject ink or to refrain from ejecting ink according to the program output of the controlling microprocessor. Each completed movement across the medium can print a swath approximately as wide as the number of nozzles arranged in a column of the ink cartridge multiplied times the distance between nozzle centers. After each such completed movement or swath the medium is moved forward the width of the swath, and the ink cartridge begins the next swath. By proper selection and timing of the signals, the desired print is obtained on the medium.
Color inkjet printers commonly employ a plurality of print cartridges, usually either two or four, mounted in the printer carriage to produce a full spectrum of colors. In a printer with four cartridges, each print cartridge contains a different color ink, with the commonly used base colors being cyan, magenta, yellow, and black. In a printer with two cartridges, one cartridge usually contains black ink with the other cartridge being a tri-compartment cartridge containing the base color cyan, magenta and yellow inks. The base colors are produced on the media by depositing a drop of the required color onto a dot location, while secondary or shaded colors are formed by depositing multiple drops of different base color inks onto the same dot location, with the overprinting of two or more base colors producing the secondary colors according to well established optical principles.
Thermal inkjet print cartridges operate by rapidly heating a small volume of ink to cause the ink to vaporize and be ejected through one of a plurality of orifices so as to print a dot of ink on a recording medium, such as a sheet of paper. Typically, the orifices are arranged in one or more linear arrays in a nozzle member. The properly sequenced ejection of ink from each orifice causes characters or other images to be printed upon the paper as the printhead is moved relative to the paper. The paper is typically shifted each time the printhead has moved across the paper. The thermal inkjet printer is fast and quiet, as only the ink strikes the paper. These printers produce high quality printing and can be made both compact and affordable.
An inkjet printhead generally includes: (1) ink channels to supply ink from an ink reservoir to each vaporization chamber proximate to an orifice; (2) a metal orifice plate or nozzle member in which the orifices are formed in the required pattern; and (3) a silicon substrate containing a series of thin film resistors, one resistor per vaporization chamber.
To print a single dot of ink, an electrical current from an external power supply is passed through a selected thin film resistor. The resistor is then heated, in turn superheating a thin layer of the adjacent ink within a vaporization chamber, causing explosive vaporization, and, consequently, causing a droplet of ink to be ejected through an associated orifice onto the paper.
In an inkjet printhead described in U.S. Pat. No. 4,683,481 to Johnson, entitled xe2x80x9cThermal Ink Jet Common-Slotted Ink Feed Printhead,xe2x80x9d ink is fed from an ink reservoir to the various vaporization chambers through an elongated hole formed in the substrate. The ink then flows to a manifold area, formed in a barrier layer between the substrate and a nozzle member, then into a plurality of ink channels, and finally into the various vaporization chambers. This design may be classified as a xe2x80x9ccenterxe2x80x9d feed design, whereby ink is fed to the vaporization chambers from a central location then distributed outward into the vaporization chambers. To seal the back of the substrate with respect to an ink reservoir so that ink flows into the center slot but is prevented from flowing around the sides of the substrate in a xe2x80x9ccenter feedxe2x80x9d design, a seal is formed, circumscribing the hole in the substrate, between the substrate itself and the ink reservoir body. Typically, this ink seal is accomplished by dispensing an adhesive bead around a fluid channel in the ink reservoir body, and positioning the substrate on the adhesive bead so that the adhesive bead circumscribes the hole formed in the substrate. The adhesive is then cured with a controlled blast of hot air, whereby the hot air heats up the substrate and adhesive, thereby curing the adhesive. This method requires quite a bit of time and thermal energy, since the heat must pass through a relatively thick substrate before heating up the adhesive. Further, because the seal line is under the substrate, it tends to be difficult to diagnose the cause of any ink leakage.
In an inkjet printhead described in U.S. Pat. No. 5,278,584 to Keefe, et al., entitled xe2x80x9cInk Delivery System for an Inkjet Printheadxe2x80x9d and U.S. application Ser. No. 08/179,866, filed Jan. 11, 1994 entitled xe2x80x9cImproved Ink Delivery System for an Inkjet Printhead,xe2x80x9d ink flows around the edges of the substrate and directly into ink the channels and then through the ink channels into the vaporization chambers. This xe2x80x9cedge feedxe2x80x9d design has a number of advantages over previous xe2x80x9ccenterxe2x80x9d feed printhead designs. One advantage is that the substrate or die width can be made narrower, due to the absence of the elongated central hole or slot in the substrate. Not only can the substrate be made narrower, but the length of the edge feed substrate can be shorter, for the same number of nozzles, than the center feed substrate due to the substrate structure now being less prone to cracking or breaking without the central ink feed hole. This shortening of the substrate enables a shorter headland and, hence, a shorter print cartridge snout. This is important when the print cartridge is installed in a printer because with a shorter print cartridge snout, the star wheels can be located closer to the pinch rollers to ensure better paper/roller contact along the transport path of the print cartridge snout. There are also a number of performance advantages to the edge feed design.
In U.S. application Ser. No. 07/862,668, filed Apr. 2, 1992, entitled xe2x80x9cIntegrated Nozzle Member and TAB Circuit for Inkjet Printhead,xe2x80x9d a novel nozzle member for an inkjet print cartridge and method of forming the nozzle member are disclosed. A flexible tape having conductive traces formed thereon has formed in it nozzles or orifices by Excimer laser ablation. The resulting nozzle member having orifices and conductive traces may then have mounted on it a substrate containing heating elements associated with each of the orifices. The conductive traces formed on the back surface of the nozzle member are then connected to the electrodes on the substrate and provide energization signals for the heating elements. A barrier layer, which may be a separate layer or formed in the nozzle member itself, includes vaporization chambers, surrounding each orifice, and ink flow channels which provide fluid communication between a ink reservoir and the vaporization chambers. By providing the orifices in the flexible circuit itself, the shortcomings of conventional electroformed orifice plates are overcome. Additionally, the orifices may be formed aligned with the conductive traces on the nozzle member so that alignment of electrodes on a substrate with respect to ends of the conductive traces also aligns the heating elements with the orifices. This integrated nozzle and tab circuit design is superior to the orifice plates for inkjet printheads formed of nickel and fabricated by lithographic electroforming processes as described in U.S. Pat. No. 4,773,971, entitled xe2x80x9cThin Film Mandrelxe2x80x9d. Such orifice plates for inkjet printheads have several shortcomings such as requiring delicate balancing of parameters such as stress and plating thicknesses, disc diameters, and overplating ratios; inherently limiting the design choices for nozzle shapes and sizes; de-lamination of the orifice plate from the substrate and corrosion by ink.
In U.S. application Ser. No. 07/864,896, filed Apr. 2, 1992, entitled xe2x80x9cAdhesive Seal for an Inkjet Printhead,xe2x80x9d a procedure for sealing an integrated nozzle and tab circuit to a print cartridge is disclosed. A nozzle member containing an array of orifices has a substrate, having heater elements formed thereon, affixed to a back surface of the nozzle member. Each orifice in the nozzle member is associated with a single heating element formed on the substrate. The back surface of the nozzle member extends beyond the outer edges of the substrate. Ink is supplied from an ink reservoir to the orifices by a fluid channel within a barrier layer between the nozzle member and the substrate. The fluid channel in the barrier layer may receive ink flowing around two or more outer edges of the substrate (xe2x80x9cedge feedxe2x80x9d) or, in another embodiment, may receive ink which flows through a hole in the center of the substrate (xe2x80x9ccenter feedxe2x80x9d). In either embodiment, the nozzle member is adhesively sealed with respect to the ink reservoir body by forming an ink seal, circumscribing the substrate, between the back surface of the nozzle member and the body.
This method and structure of providing a seal directly between a nozzle member and an ink reservoir body has many advantages over prior art methods of providing a seal between the back surface of the substrate and the ink reservoir body. One advantage is that such a seal makes an edge ink-feed design possible. Another advantage is that, in an embodiment where the nozzle member has conductive traces formed on its bottom surface for contact to electrodes on the substrate, the adhesive seal acts to encapsulate and protect the traces near the substrate which may come in contact with ink. Additionally, since the sealant is also an adhesive, the nozzle member is directly secured to the ink reservoir body, thus forming a stronger bond between the printhead and the inkjet print cartridge. Further, it is much easier to detect leaks in the sealant, since the sealant line is more readily observable. Another advantage is that it takes less time to cure the adhesive seal, since only a thin nozzle member is between the sealant and the heat source used for curing the sealant.
However, during manufacturing, the headland design of previous print cartridges had several disadvantages, including difficulty in controlling the edge seal to the die or substrate without having adhesive getting into the nozzle and clogging them, or on the other hand, voids of adhesive in the tab bond window. It was also very difficult to control the adhesive bulge through the window caused by excess adhesive, or varying die placement. All of these problems result in extremely high yield losses when manufacturing thermal inkjet print cartridges. In U.S. application Ser. No. 08/398,849, filed Mar. 6, 1995, entitled xe2x80x9cInkjet Cartridge Design for Facilitating the Adhesive Sealing of a Printhead to an Ink Reservoirxe2x80x9d an improved headland design is disclosed which alleviates the above-mentioned problems.
However, the above designs did not address the problem of xe2x80x9cdimplingxe2x80x9d being formed in the nozzle member caused by bending of the nozzle member due to the stresses created by the adhesive process of sealing the nozzle member to the print cartridge. This dimpling of the nozzle member creates poor nozzle camber angle (NCA), thereby skewing the nozzles, which causes trajectory errors for the ejected ink droplets from the nozzles. When the TAB head assembly is scanned across a recording medium the ink trajectory errors will affect the location of printed dots and, thus, affect the quality and/or speed of printing.
One method of reducing this problem is using an articulated flex. This involves using laser ablation to remove material from the flex circuit in order to increase flexibility along a crease parallel to the firing chamber array. The disadvantage of this method is that structural integrity of printhead assembly in vicinity of firing chambers is reduced. Also, costs are increased due to the additional and/or modified laser ablation steps. Another method is xe2x80x9cwindowframingxe2x80x9d, which involves bonding THA to a stiff frame for maintaining the flex circuit in tension. This method has several problems, namely additional part and processes are required, the amount of tension required to affect the NCA causes delamination of the flex circuit and the barrier layer and this method requires electrical isolation from copper traces on flex circuit. Yet another method includes using a diamond light coating (DLC). The DLC method involves applying a hard coating to one or both sides of the flex circuit. However, this method has increased costs, causes cracking of the coating and provides minimal effectiveness on NCA.
Accordingly, it would be advantageous to have an improved print cartridge that reduces dimple in the nozzle member and the attendant nozzle trajectory errors.
The present invention provides an improved method and design for a printing system and print cartridge for reducing dimpling in the nozzle member and attendant nozzle trajectory errors. In a preferred embodiment, a nozzle member has a plurality of ink orifices formed therein by suitable processing techniques. A substrate containing a plurality of heating elements and associated ink ejection chambers is affixed to the nozzle member via suitable processing with a suitable adhesive. The heating elements are mounted on a back surface of the nozzle member, each heating element being located proximate to an associated ink ejection chamber and ink orifice, with the back surface of the nozzle member extending over two or more outer edges of the substrate. The nozzle member includes reinforcing features. These features increase the structural integrity of flex circuit in the vicinity of the orifices. The reinforcing features can be of any suitable shape for aiding in maintaining plastic deformation of the flex material in the vicinity of the orifices during preprocessing of the flexible circuit.
The invention further includes a method for creating the reinforcing features by selectively embossing the flex circuit either before, after, or during the creation of the orifices of the nozzle member.